1. Field of the Invention
The present invention relates to a flat panel type display device of such as a color liquid crystal display device and, in particular, the present invention relates to a flat panel type display device constructed such that unnecessary electromagnetic radiation, which may bring about EMI (Electro-magnetic Interference), etc., is restricted.
2. Description of the Prior Art
As a flat panel type display device, a color liquid crystal display device of an active matrix system, for example, includes a liquid crystal display panel and a backlight for illuminating a lower surface of the liquid crystal display panel. A horizontal drive circuit substrate and a vertical drive circuit substrate are arranged outside an outer peripheral portion of the liquid crystal display panel. Further, a signal processing substrate for converting an externally supplied image signal into a horizontal drive signal and supplying the latter signal to a liquid crystal driving IC on the horizontal drive circuit substrate by way of a connecting substrate is arranged on a rear surface side of the liquid crystal display panel. The liquid crystal display panel, the backlight and the horizontal and vertical drive circuit substrates are accommodated in a casing constructed with a front shield plate, which is formed of a metal and has a display window, and a metal rear shield plate for accommodating and holding the backlight.
FIG. 1A is a perspective view of an example of a conventional liquid crystal display device, illustrating a positional relation between a liquid crystal display panel, a horizontal drive circuit substrate and a signal processing substrate thereof and FIG. 1B is a plan view of the signal processing substrate and a connecting unit for connecting the horizontal liquid crystal display panel to the signal processing substrate, which are extended in a plane. Further, FIG. 2A and FIG. 2B are cross sections taken along a line Axe2x80x94Axe2x80x2 in FIG. 1A, illustrating a portion of a second shield plate, which has no nail portion for fixing the connecting substrate to the second shield plate and a portion thereof, which has a nail portion provided appropriately, respectively. Incidentally, in order to simplify the illustration, the vertical drive circuit substrate, the front shield plate, the rear shield plate and the backlight, etc, are not shown in FIG. 1A. FIG. 3 is a cross section taken along a line Bxe2x80x94Bxe2x80x2 in FIG. 1A.
Referring to FIG. 1A to FIG. 3, the conventional liquid crystal display device 510 is constructed with the liquid crystal display panel 511, a front shield plate 531, a first rear shield plate 533, a second rear shield plate 534, the signal processing substrate 521, the horizontal drive circuit substrate 524 in the form of a TCP (Tape Carrier Package) on which horizontal driving IC""s 526 are mounted, the connecting substrate 523, a flexible printed circuit substrate (referred to as FPC, hereinafter) 522 and a light diffusing plate 513 for uniformly dispersing light from the backlight (not shown), etc. Incidentally, the horizontal drive circuit substrate 524 will be referred to as TCP, hereinafter.
A peripheral portion of the display panel 511, which is a non-display region, is sandwiched between the front shield plate 531 and the second rear shield plate 534 by way of a first spacer 546 and a second spacer plate 547, respectively. The light diffusing plate 513 received and held by the first rear shield plate 533 and the backlight (not shown) are provided on the side of a rear surface (opposite to a display surface) of the liquid crystal display panel 511.
As shown in FIG. 3, the signal processing substrate 521 is fixed to a rear surface side of the first rear shield plate 533 via an insulating sheet 555 and the connecting substrate 523 is fixed to the second rear shield plate 534 in a plane substantially perpendicular to the display surface of the liquid crystal display panel 511 via the insulating sheet 551. This fixation of the connecting substrate 523 is performed by at least one nail portion 537 provided in an appropriate portion of the second rear shield plate 534, as shown in FIG. 2B. The portion of the second rear shield plate 534 in which the nail portion 537 is provided corresponds to a region of the connecting substrate 523 in which any wiring pattern is not formed. Incidentally, a connecting unit 520 for connecting the signal processing substrate 521 to the liquid crystal display panel 511 includes the FPC 522, the connecting substrate 523 and the TCP 524, as shown in FIG. 1B.
One end of the TCP 524 (on the output end side) is bonded to electrodes provided in an edge portion of the liquid crystal display panel 511 by thermocompression bonding with using, for example, a thermoplastic, anisotropic electrically conductive film and the other end (input end side) thereof is connected to the connecting substrate 523 by, for example, soldering. The connecting substrate 523 and the signal processing substrate 521 are connected to each other by the FPC 522.
Incidentally, an outer casing (not shown) having at least an electrically conductive inner surface portion and covering the whole rear surface of the liquid crystal display panel including the signal processing substrate 521 is provided on the rear surface side of the liquid crystal display device 510. The front shield plate, the first rear shield plate and the second rear shield plate are connected to the inner surface portion of the outer casing.
In the conventional liquid crystal display device 510 described above, an electromagnetic shield structure for restricting EMI, etc., due to unnecessary electromagnetic radiation from electronic parts and wiring mounted on the signal processing substrate 521, the TCP 524 and/or the vertical driving circuit substrate, which is not shown, etc., is formed by connecting at least the electrically conductive inner surface portion of the outer casing covering these components to a common ground terminal (not shown) of the liquid crystal display device 510.
However, with the recent tendency of increase of the operating frequency, particularly, the horizontal driving frequency, of the liquid crystal display device, unnecessary electromagnetic radiation becomes a problem in, particularly, the connecting substrate 523 in which a number of horizontal drive signals are transmitted along a long wiring within a limited region. As shown in FIG. 2A, FIG. 2B and FIG. 3, the connecting substrate 523 is fixed to the second rear shield pate 534 via the thin insulating sheet 551 and, therefore, the electric insulation is maintained. However, it has been found that, when a number of high frequency signals flow in the connecting substrate 523, the signals are leaked between the first rear shield plate 533 and the second rear shield plate 534 by such as capacitive coupling and unnecessary electromagnetic radiation occurs through the first rear shield plate 533 and the second rear shield plate 534 as an antenna.
An object of the present invention is to provide a display device such as a color liquid crystal display device having a structure with which unnecessary electromagnetic radiation, which may cause EMI, etc., can be restricted even when a number of high frequency signals are transmitted through a long wiring in a connecting substrate having limited wiring space.
In order to achieve the above object, the display device according to the present invention is featured by comprising at least a display unit for displaying an image on a front surface of the display unit, a signal processing unit for processing an externally supplied image signal and outputting a first signal for displaying the image, a drive unit for receiving the first signal and outputting a second signal for driving the display unit, a connecting unit for connecting the signal processing unit to the display unit, a first shield unit formed of an electrically conductive material such as metal and having an opening portion corresponding to an image displaying region of the display unit, for electromagnetically shielding a peripheral region and a side face region of the image display surface and a second shield unit formed of an electrically conductive material such as metal, etc., for electromagnetically shielding a whole rear side surface of the display unit. The connecting unit comprises a first flexible connecting portion connected to the signal processing unit, a second flexible connecting portion connected to the display unit and mounting the drive unit thereon and a connecting substrate for connecting the first flexible connecting portion and the second flexible connecting portion to each other, the connecting substrate being kept in a position between the first shield unit and the second shield unit separated from the first and second shield units by predetermined distances, respectively.
It is referable that, representing the distance between the first shield unit and the second shield unit arranged on the connecting substrate by L and distances between a center of the connecting substrate in thickness direction and the first shield unit and the second shield unit by d1 and d2, respectively, d1 and d2 satisfy the following relations to L:
d1xe2x89xa70.4xc3x97L and d2xe2x89xa70.4xc3x97L.
The display device may further comprise a first support member for supporting a portion between the connecting substrate and the first shield unit and a second support member for supporting a portion between the connecting substrate and the second shield unit. Heights of the first and second support members are equal to each other. The first support member and the second support member are preferably formed of electrically non-conductive material such as silicon rubber.
The display unit may be a liquid crystal display panel composed of two substrates opposing to each other with a predetermined gap therebetween and liquid crystal material layer arranged between the two substrates.